The invention relates to indicating devices generally and more particularly to micro-miniature indicators which are capable of visually displaying the presence in a system of either of two conditions, such as favorable or unfavorable.
The prior art includes a wide variety of apparatus of this general type. The apparatus may be categorized in terms of the shape of the indicating element. U.S. Pat. No. 3,671,900 shows a typical cylindrical or round indicating element. The invention has particular application to a ball-shaped indicating element although it will be understood to also have applications to other indicating devices. Ball-shaped indicating elements are shown in U.S. Pat. Nos. 3,872,469; 4,128,825 and 3,487,403. The latter patent illustrates apparatus utilizing two discrete balls which are serially operated to provide a visual indication. The disadvantage of this apparatus is that it is relatively complex and accordingly more expensive and difficult to assemble and manufacture.
The difficulty with assembling the devices in accordance with the invention is particularly acute because of the relatively small size of the apparatus. Such apparatus is ordinarily manufactured to Mil Spec I-83287/3 which specifies a maximum length exclusive of terminals of 1.09 inches. The apparatus in accordance with the invention is ordinarily utilized in an environment in which there is substantial vibration as in airplanes.
It is an object of the invention to provide apparatus which will substantially eliminate indication changes as a result of vibration.
It is another object of the invention to provide apparatus which will avoid mechanical stops which tends to increase the sensitivity of the apparatus to vibration because of the transfer of energy from the stop to the indicating element.
it is another object of the invention to provide apparatus which is simple and as inexpensive as possible to manufacture consistent with the object of preventing accidental change in indication.